Python

Format Bytes / Duration Human-Readable

Two formatting helpers everyone re-implements: bytes → "1.5 MB", seconds → "1h 23m 45s". Base-1024 IEC units by default for bytes.

5h ago 0

JavaScript

Worker Pool (Web Workers)

Manages a pool of Web Workers for CPU-intensive tasks (image processing, crypto, parsing). Distributes tasks across available workers using a round-robin strategy and returns a Promise per task. Falls back gracefully to inline execution in environments where workers are unavailable.

5h ago 0

JavaScript

Validate URL

Validates whether a string is a well-formed URL using the native URL constructor, which matches browser parsing behaviour exactly. Optionally restricts to specific protocols (defaults to http and https). No regex maintenance required — if the browser can parse it as a URL, this returns true.

5h ago 0

JavaScript

WeakRef Object Cache

A cache backed by WeakRef and FinalizationRegistry. Stored values are held weakly — the garbage collector can reclaim them if memory pressure is high, and the registry automatically cleans up stale entries from the internal map. Ideal for caching large objects (DOM nodes, rendered images) without causing memory leaks.

5h ago 0

Java

Sealed Classes + Pattern Matching (Java 21+)

`sealed` restricts which classes can extend a type — perfect for closed hierarchies that pattern matching can switch over exhaustively. The compiler enforces that you handle every variant.

5h ago 0

Rust

HashMap with the entry() API

The `entry()` API is the idiomatic way to "insert if absent" or "update if present" in a single lookup. Avoids double-lookups that the explicit `contains_key` + `insert` dance would need.

5h ago 0

Go

Crypto-Random Bytes + Hex/Base64

`crypto/rand` is the cryptographic CSPRNG. Use it for tokens, session IDs, API keys, password salts — anywhere `math/rand` would be a security bug.

5h ago 0

SQL

UPDATE with JOIN

Update one table using values from another. Syntax varies by database — PostgreSQL uses `FROM`, MySQL puts the join in the `UPDATE` clause.

5h ago 0

Go

sync.Mutex vs sync.RWMutex

`Mutex` allows one goroutine at a time — for both reads and writes. `RWMutex` allows multiple concurrent readers OR one writer — much better when reads dominate.

5h ago 0

Go

SHA-256 Hash of File or String

`crypto/sha256` is the canonical hash. Use the streaming `Hash` interface for files — never load multi-GB content into memory just to hash it.

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PHP

Human-Readable File Size

Format a byte count as a human-friendly string (KB / MB / GB / TB). Defaults to base-1024 sizes; pass base 1000 for SI units.

5h ago 0

Bash

Generate SSH Keypair Non-Interactively

ssh-keygen normally prompts. Pass -N "" for empty passphrase, -f for the path, -t ed25519 for modern key type. Idempotent — skip if a key already exists.

5h ago 0

Go

select — Multiplex Channel Operations

`select` is like a switch for channels — runs whichever case is ready. Use `default` for non-blocking sends/receives; `case <-time.After(d)` for timeouts.

5h ago 0

Go

Worker Pool with Channels

Spawn N worker goroutines, feed them tasks over a jobs channel, collect results on a results channel. Idiomatic Go pattern for bounded concurrency.

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Go

context.WithValue — Request-Scoped Values

Attach data to a context that flows down through your call chain — request IDs, authenticated user, trace spans. Use a private key type to avoid collisions across packages.

5h ago 0

PHP

Stream Large CSV with Generator

Iterate over a CSV file row-by-row without ever loading the whole file into memory. Uses a generator so consumers can foreach naturally and PHP cleans up the file handle.

5h ago 0

PHP

Validate URL (scheme + host)

Beyond filter_var, also require the URL to have an http(s) scheme and a non-empty host. Rejects "javascript:" and other risky pseudo-schemes commonly seen in stored XSS.

5h ago 0

Go

Channels — Basics

Channels are typed pipes between goroutines. Unbuffered = synchronous handoff; buffered = up to N values queued. Close a channel to signal "no more values" — receivers see ok=false.

5h ago 0

Go

Fan-Out / Fan-In

Distribute work across N workers (fan-out), then merge their results back into one channel (fan-in). Used when you can't process items strictly in order but want to retain output as one stream.

5h ago 0

Java

Semaphore — Bounded Concurrency

Limit how many threads can enter a critical section. `acquire()` blocks until a permit is available; `release()` returns one. Use for rate limits, connection pools, or any "max N at a time" pattern.

5h ago 0

TypeScript

Concurrency Limiter (semaphore)

Run an array of async tasks but limit concurrency to N at a time — like p-limit, in 30 lines. Preserves input order in the output array.

5h ago 0

Bash

Idempotent Append to File

Add a line to a file (e.g., a config or PATH export) only if it isn't already present. Common in install/setup scripts that need to be safe to re-run.

5h ago 0

Bash

HMAC-SHA256 with openssl

Sign a payload with a shared secret for webhook verification (Stripe, GitHub, etc.). openssl reads the input from stdin or -in.

5h ago 0

Rust

CSV Read/Write with the csv Crate

`csv` + `serde` lets you read/write CSVs directly into typed structs. No manual field parsing; column order tolerant via headers.

5h ago 0

Go

Goroutine Leak Prevention

A goroutine that's blocked forever on a channel send/receive leaks — it's never garbage-collected. Always pair channels with `select { case <-ctx.Done(): return }` to give them an exit path.

5h ago 0

PHP

Find Files Modified in Last N Days

List every file under a directory that was modified within the last N days. Useful for incremental backups or detecting stale entries.

5h ago 0

PHP

Encrypt / Decrypt with libsodium

Symmetric AEAD encryption using the libsodium "secretbox" (XSalsa20-Poly1305). Built into PHP since 7.2 — no extension needed. Returns base64 ciphertext with the nonce prepended.

5h ago 0

Go

errgroup — Fan-Out with Cancellation

`golang.org/x/sync/errgroup` runs N goroutines, returns the first error, and cancels the others via a shared context. The right pattern for parallel I/O where any failure should abort the rest.

5h ago 0

PHP

Format Money with Currency

Format an amount of cents as a localized currency string using NumberFormatter from intl. Falls back to a basic sprintf if intl isn't available.

5h ago 0

Python

chunked — Split Iterable into Fixed-Size Pieces

Lazy chunker that works on any iterable, not just lists. Common building block for batch APIs — "send 50 rows per request" — without loading the source into memory.

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